System and method for minimally invasive cutting instrument operation

ABSTRACT

Techniques for operating an instrument include a computer-assisted device having one or more processors, a motor or other active actuator, and an articulated arm configured to support the instrument having a cutting blade. The one or more processors are configured to control, using the motor or other active actuator, the instrument according to a force or torque limit profile. The force or torque limit profile includes a first force or torque limit used when extending the cutting blade from a first position to a second position, a second force or torque limit used when retracting the cutting blade from the second position to a third position between the first position and the second position and further retracting the cutting blade to the first position, and a third force or torque limit used while the cutting blade is in the first position.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 17/102,210 (filed Nov. 23, 2020), which is divisional of U.S.patent application Ser. No. 15/573,096 (filed on Nov. 9, 2017), which isa U.S. National Stage patent application of International PatentApplication No. PCT/US2016/032351 (filed on May 13, 2016), the benefitof which is claimed, and claims priority to and the benefit of thefiling date of U.S. Provisional Patent Application 62/162,217, entitled“SYSTEM AND METHOD FOR MINIMALLY INVASIVE CUTTING INSTRUMENT OPERATION”and filed May 15, 2015, each of which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to operation of devices witharticulated arms and end effectors and more particularly to operation ofa minimally invasive cutting instrument.

BACKGROUND

More and more devices are being replaced with autonomous andsemiautonomous electronic devices. This is especially true in thehospitals of today with large arrays of autonomous and semiautonomouselectronic devices being found in operating rooms, interventionalsuites, intensive care wards, emergency rooms, and the like. Forexample, glass and mercury thermometers are being replaced withelectronic thermometers, intravenous drip lines now include electronicmonitors and flow regulators, and traditional hand-held surgicalinstruments are being replaced by computer-assisted medical devices.

Minimally invasive surgical techniques using computer-assisted medicaldevices generally attempt to perform surgical and/or other procedureswhile minimizing damage to healthy tissue. Some minimally invasiveprocedures may be performed remotely through the use ofcomputer-assisted medical devices with surgical instruments. With manycomputer-assisted medical devices, a surgeon and/or other medicalpersonnel may typically manipulate input devices using one or morecontrols on an operator console. As the surgeon and/or other medicalpersonnel operate the various controls at the operator console, thecommands are relayed from the operator console to a patient side deviceto which one or more end effectors and/or surgical instruments aremounted. In this way, the surgeon and/or other medical personnel areable to perform one or more procedures on a patient using the endeffectors and/or surgical instruments. Depending upon the desiredprocedure and/or the surgical instruments in use, the desired proceduremay be performed partially or wholly under control of the surgeon and/ormedical personnel using teleoperation and/or under semi-autonomouscontrol where the surgical instrument may perform a sequence ofoperations based on one or more activation actions by the surgeon and/orother medical personnel.

Minimally invasive surgical instruments, whether actuated manually,teleoperatively, and/or semi-autonomously may be used in a variety ofoperations and/or procedures and may have various configurations. Manysuch instruments include an end effector mounted at a distal end of ashaft that may be mounted to the distal end of an articulated arm. Inmany operational scenarios, the shaft may be configured to be inserted(e.g., laparoscopically, thoracoscopically, and/or the like) through anopening (e.g., a body wall incision, a natural orifice, and/or the like)to reach a remote surgical site. In some instruments, an articulatingwrist mechanism may be mounted to the distal end of the instrument'sshaft to support the end effector with the articulating wrist providingthe ability to alter an orientation of the end effector relative to alongitudinal axis of the shaft.

End effectors of different design and/or configuration may be used toperform different tasks, procedures, and functions so as to be allow thesurgeon and/or other medical personnel to perform any of a variety ofsurgical procedures. Examples include, but are not limited to,cauterizing, ablating, suturing, cutting, stapling, fusing, sealing,etc., and/or combinations thereof. Accordingly, end effectors caninclude a variety of components and/or combinations of components toperform these surgical procedures.

Consistent with the goals of a minimally invasive procedure, the size ofthe end effector is typically kept as small as possible while stillallowing it to perform its intended task. One approach to keeping thesize of the end effector small is to accomplish actuation of the endeffector through the use of one or more inputs at a proximal end of thesurgical instrument, which is typically located externally to thepatient. Various gears, levers, pulleys, cables, rods, bands, and/or thelike, may then be used to transmit actions from the one or more inputsalong the shaft of the surgical instrument and to actuate the endeffector. In the case of a computer-assisted medical device with anappropriate surgical instrument, a transmission mechanism at theproximal end of the instrument interfaces with various motors,solenoids, servos, active actuators, hydraulics, pneumatics, and/or thelike provided on an articulated arm of the patient side device or apatient side cart. The motors, solenoids, servos, active actuators,hydraulics, pneumatics, and/or the like typically receive controlsignals through a master controller and provide input in the form offorce and/or torque at the proximal end of the transmission mechanism,which the various gears, levers, pulleys, cables, rods, bands, and/orthe like ultimately transmit to actuate the end effector at the distalend of the transmission mechanism.

Because of the remote nature of the operation of such end effectors, itmay be difficult in some cases for the surgeon and/or other medicalpersonnel to know the position of one or more components of the endeffector during actuation to perform a desired procedure. For example,in some cases, other portions of the surgical instrument, including theend effector itself, and/or parts of the anatomy of the patient may hidefrom view one or more components of the surgical instrument during theactuation of the one or more components. Additionally, when one or moreof the components encounters a fault condition while attempting toperform the desired procedure, it may be difficult for the surgeonand/or other medical personnel to detect and/or correct the faultcondition due to the limited visibility of the end effector, the limitedspace in which the surgical instrument operates, the limited access tothe surgical instrument, the remote position of the end effectorrelative to the surgeon and/or other medical personnel, and/or the like.

In addition, safety conditions may also be a factor in the design and/oroperation of the surgical instrument. In some examples, the end effectorof a surgical tool, such as a cutting tool, may include a sharp cuttingblade. When the cutting blade is not actively being used to cut, thecutting blade may be sheathed and/or garaged within a housing on the endeffector so that it is generally positioned where it cannot accidentallycut tissue of the patient and/or medical personnel manipulating thesurgical tool during non-operation. Similarly, one or more delicatecomponents of the end effector may also be sheathed and/or garaged toprevent damage to the delicate components during non-operation.

Accordingly, improved methods and systems for the operation of surgicalinstruments, such as a cutting instrument, are desirable. In someexamples, it may be desirable to provide automated control of thesurgical instrument so as to help ensure that the surgical instrumentmay be able to successfully perform a desired procedure. In someexamples, it may be desirable to provide a configuration of the surgicalinstrument that supports safety to the patient and/or medical personneland protection to the surgical instrument during both operation andnon-operation.

SUMMARY

Consistent with some embodiments, a surgical cutting instrument for usewith a computer-assisted medical device. The surgical cutting instrumentincludes a drive unit, an end effector located at a distal end of theinstrument, a shaft between the drive unit and the end effector, and agarage for housing the cutting blade when the cutting blade is not inuse. The end effector includes opposable gripping jaws and a cuttingblade. The shaft houses one or more drive mechanisms for coupling forceor torque from the drive unit to the end effector. To perform a cuttingoperation, the instrument is configured to extend the cutting blade froma first position to a second position, retract the cutting blade fromthe second position to a third position between the first and secondpositions, and further retract the cutting blade to the first position.While the cutting blade is not in use, the cutting blade is maintainedin the first position using a restraining mechanism in the drive unit,force or torque applied by a motor or other active actuator to the driveunit, or both.

Consistent with some embodiments, a method of performing a cuttingoperation using a surgical cutting instrument for use with acomputer-assisted medical device includes holding a cutting blade of anend effector in a first position when the cutting blade is not in use,extending the cutting blade from the first position to a second positionby applying force or torque to the drive unit, retracting the cuttingblade from the second position to a third position between the first andsecond positions, and further retracting the cutting blade to the firstposition. The holding of the cutting blade in the first position isperformed by a restraining mechanism of a drive unit, a force or torqueapplied to the drive unit by a motor or active actuator, or both. Theextending and retracting comprise applying force or torque to the driveunit using the motor or active actuator.

Consistent with some embodiments, a non-transitory machine-readablemedium includes a plurality of machine-readable instructions which whenexecuted by one or more processors associated with a computer-assistedmedical device are adapted to cause the one or more processors toperform a method. The method includes holding a cutting blade of an endeffector in a first position when the cutting blade is not in use,extending the cutting blade from the first position to a second positionby applying force or torque to the drive unit, retracting the cuttingblade from the second position to a third position between the first andsecond positions, and further retracting the cutting blade to the firstposition. The holding the cutting blade in the first position isperformed by a restraining mechanism of a drive unit, a force or torqueapplied to the drive unit by a motor or active actuator, or both. Theextending and retracting includes applying force or torque to the driveunit using the motor or active actuator.

Consistent with some embodiments, a computer-assisted medical deviceincludes one or more processors, an articulated arm, a motor or otheractive actuator, and a surgical instrument coupled to a distal end ofthe articulated arm. The surgical instrument includes a drive unitlocated at a proximal end of the surgical instrument, an end effectorlocated at a distal end of the surgical instrument, a shaft between thedrive unit and the end effector, and a garage for housing the cuttingblade when the cutting blade is not in use. The end effector comprisingopposable gripping jaws and a cutting blade. The shaft houses one ormore drive mechanisms for coupling force or torque from the drive unitto the end effector. The computer-assisted medical device is configuredto perform a cutting operation using the cutting blade by extending thecutting blade from a first position to a second position, retracting thecutting blade from the second position to a third position between thefirst and second positions, and further retracting the cutting blade tothe first position. While the cutting blade is not in use, the cuttingblade is maintained in the first position using a restraining mechanismin the drive unit, force or torque applied by the motor or other activeactuator to the drive unit, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a computer-assisted system accordingto some embodiments.

FIG. 2 is a simplified diagram showing a minimally invasive surgicalinstrument according to some embodiments.

FIG. 3 is a simplified perspective diagram of the distal end of thesurgical instrument of FIG. 2 according to some embodiments.

FIGS. 4A-4C are simplified cut-away diagrams of the end effector ofFIGS. 2 and 3 according to some embodiments.

FIG. 5 is a simplified perspective diagram of a drive unit for a degreeof freedom according to some embodiments.

FIG. 6 is a simplified diagram of a positional profile and acorresponding torque limit profile for a cutting operation according tosome embodiments.

FIG. 7 is a simplified diagram of a method for performing a cuttingoperation according to some embodiments.

In the figures, elements having the same designations have the same orsimilar functions.

DETAILED DESCRIPTION

In the following description, specific details are set forth describingsome embodiments consistent with the present disclosure. It will beapparent to one skilled in the art, however, that some embodiments maybe practiced without some or all of these specific details. The specificembodiments disclosed herein are meant to be illustrative but notlimiting. One skilled in the art may realize other elements that,although not specifically described here, are within the scope and thespirit of this disclosure. In addition, to avoid unnecessary repetition,one or more features shown and described in association with oneembodiment may be incorporated into other embodiments unlessspecifically described otherwise or if the one or more features wouldmake an embodiment non-functional.

FIG. 1 is a simplified diagram of a computer-assisted system 100according to some embodiments. As shown in FIG. 1 , computer-assistedsystem 100 includes a computer-assisted device 110 with one or moremovable or articulated arms 120. Each of the one or more articulatedarms 120 may support one or more instruments 130. In some examples,computer-assisted device 110 may be consistent with a computer-assistedsurgical device. The one or more articulated arms 120 may each providesupport for medical instruments 130 such as surgical instruments,imaging devices, and/or the like. In some examples, the instruments 130may include end effectors that are capable of, but are not limited to,performing, gripping, retracting, cauterizing, ablating, suturing,cutting, stapling, fusing, sealing, etc., and/or combinations thereof.

Computer-assisted device 110 may further be coupled to an operatorworkstation (not shown), which may include one or more master controlsfor operating the computer-assisted device 110, the one or morearticulated arms 120, and/or the instruments 130. In some examples, theone or more master controls may include master manipulators, levers,pedals, switches, keys, knobs, triggers, and/or the like. In someembodiments, computer-assisted device 110 and the operator workstationmay correspond to a da Vinci® Surgical System commercialized byIntuitive Surgical, Inc. of Sunnyvale, California. In some embodiments,computer-assisted surgical devices with other configurations, fewer ormore articulated arms, and/or the like may be used withcomputer-assisted system 100.

Computer-assisted device 110 is coupled to a control unit 140 via aninterface. The interface may include one or more cables, fibers,connectors, and/or buses and may further include one or more networkswith one or more network switching and/or routing devices. Control unit140 includes a processor 150 coupled to memory 160. Operation of controlunit 140 is controlled by processor 150. And although control unit 140is shown with only one processor 150, it is understood that processor150 may be representative of one or more central processing units,multi-core processors, microprocessors, microcontrollers, digital signalprocessors, field programmable gate arrays (FPGAs), application specificintegrated circuits (ASICs), and/or the like in control unit 140.Control unit 140 may be implemented as a stand-alone subsystem and/orboard added to a computing device or as a virtual machine. In someembodiments, control unit 140 may be included as part of the operatorworkstation and/or operated separately from, but in coordination withthe operator workstation.

Memory 160 may be used to store software executed by control unit 140and/or one or more data structures used during operation of control unit140. Memory 160 may include one or more types of machine readable media.Some common forms of machine readable media may include floppy disk,flexible disk, hard disk, magnetic tape, any other magnetic medium,CD-ROM, any other optical medium, punch cards, paper tape, any otherphysical medium with patterns of holes, RAM, PROM, EPROM, FLASH-EPROM,any other memory chip or cartridge, and/or any other medium from which aprocessor or computer is adapted to read.

As shown in FIG. 1 , memory 160 includes a control application 170 thatmay be used to support autonomous, semiautonomous, and/or teleoperatedcontrol of computer-assisted device 110. Control application 170 mayinclude one or more application programming interfaces (APIs) forreceiving position, motion, force, torque, and/or other sensorinformation from computer-assisted device 110, articulated arms 120,and/or instruments 130, exchanging position, motion, force, torque,and/or collision avoidance information with other control unitsregarding other devices, and/or planning and/or assisting in theplanning of motion for computer-assisted device 110, articulated arms120, and/or instruments 130. In some examples, control application 170may further support autonomous, semiautonomous, and/or teleoperatedcontrol of the instruments 130 during a surgical procedure. And althoughcontrol application 170 is depicted as a software application, controlapplication 170 may be implemented using hardware, software, and/or acombination of hardware and software.

In some embodiments, computer-assisted system 100 may be found in anoperating room and/or an interventional suite. And althoughcomputer-assisted system 100 includes only one computer-assisted device110 with two articulated arms 120 and corresponding instruments 130, oneof ordinary skill would understand that computer-assisted system 100 mayinclude any number of computer-assisted devices with articulated armsand/or instruments of similar and/or different in design fromcomputer-assisted device 110. In some examples, each of thecomputer-assisted devices may include fewer or more articulated armsand/or instruments.

FIG. 2 is a simplified diagram showing a minimally invasive surgicalinstrument 200 according to some embodiments. In some embodiments,surgical instrument 200 may be consistent with any of the instruments130 of FIG. 1 . The directions “proximal” and “distal” as depicted inFIG. 2 and as used herein help describe the relative orientation andlocation of components of surgical instrument 200. Distal generallyrefers to elements in a direction further along a kinematic chain from abase of a computer-assisted device, such as computer-assisted device110, and/or or closest to the surgical work site in the intendedoperational use of the surgical instrument 200. Proximal generallyrefers to elements in a direction closer along a kinematic chain towardthe base of the computer-assisted device and/or one of the articulatedarms of the computer-assisted device.

As shown in FIG. 2 , surgical instrument 200 includes a long shaft 210used to couple an end effector 220 located at a distal end of shaft 210to where the surgical instrument 200 is mounted to an articulated armand/or a computer-assisted device at a proximal end of shaft 210.Depending upon the particular procedure for which the surgicalinstrument 200 is being used, shaft 210 may be inserted through anopening (e.g., a body wall incision, a natural orifice, and/or the like)in order to place end effector 220 in proximity to a remote surgicalsite located within the anatomy of a patient. As further shown in FIG. 2, end effector 220 is generally consistent with a two-jawedgripper-style end effector, which in some embodiments may furtherinclude a cutting and/or a fusing or sealing mechanism as is describedin further detail below with respect to FIGS. 3 and 4A-4C. However, oneof ordinary skill would understand that different surgical instruments200 with different end effectors 220 are possible and may be consistentwith the embodiments of surgical instrument 200 as described elsewhereherein.

A surgical instrument, such as surgical instrument 200 with end effector220 typically relies on multiple degrees of freedom (DOFs) during itsoperation. Depending upon the configuration of surgical instrument 200and the articulated arm and/or computer-assisted device to which it ismounted, various DOFs that may be used to position, orient, and/oroperate end effector 220 are possible. In some examples, shaft 210 maybe inserted in a distal direction and/or retreated in a proximaldirection to provide an insertion DOF that may be used to control howdeep within the anatomy of the patient that end effector 220 is placed.In some examples, shaft 210 may be able rotate about its longitudinalaxis to provide a roll DOF that may be used to rotate end effector 220.In some examples, additional flexibility in the position and/ororientation of end effector 220 may be provided by an articulated wrist230 that is used to couple end effector 220 to the distal end of shaft210. In some examples, articulated wrist 230 may include one or morerotational joints, such as one or more roll, pitch or yaw joints thatmay provide one or more “roll,” “pitch,” and “yaw” DOF(s), respectively,that may be used to control an orientation of end effector 220 relativeto the longitudinal axis of shaft 210. In some examples, the one or morerotational joints may include a pitch and a yaw joint; a roll, a pitch,and a yaw joint, a roll, a pitch, and a roll joint; and/or the like. Insome examples, end effector 220 may further include a grip DOF used tocontrol the opening and closing of the jaws of end effector 220 and/oran activation DOF used to control the extension, retraction, and/oroperation of a cutting mechanism as is described in further detailbelow.

Surgical instrument 200 further includes a drive system 240 located atthe proximal end of shaft 210. Drive system 240 includes one or morecomponents for introducing forces and/or torques to surgical instrument200 that may be used to manipulate the various DOFs supported bysurgical instrument 200. In some examples, drive system 240 may includeone or more motors, solenoids, servos, active actuators, hydraulicactuators, pneumatic actuators, and/or the like that are operated basedon signals received from a control unit, such as control unit 140 ofFIG. 1 . In some examples, the signals may include one or more currents,voltages, pulse-width modulated wave forms, and/or the like. In someexamples, drive system 240 may include one or more shafts, gears,pulleys, rods, bands, and/or the like which may be coupled tocorresponding motors, solenoids, servos, active actuators, hydraulics,pneumatics, and/or the like that are part of the articulated arm, suchas any of the articulated arms 120, to which surgical instrument 200 ismounted. In some examples, the one or more drive inputs, such as shafts,gears, pulleys, rods, bands, and/or the like, may be used to receiveforces and/or torques from the motors, solenoids, servos, activeactuators, hydraulics, pneumatics, and/or the like and apply thoseforces and/or torques to adjust the various DOFs of surgical instrument200.

In some embodiments, the forces and/or torques generated by and/orreceived by drive system 240 may be transferred from drive system 240and along shaft 210 to the various joints and/or elements of surgicalinstrument 200 located distal to drive system 240 using one or moredrive mechanisms 250. In some examples, the one or more drive mechanisms250 may include one or more gears, levers, pulleys, cables, rods, bands,and/or the like. In some examples, shaft 210 is hollow and the drivemechanisms 250 pass along the inside of shaft 210 from drive system 240to the corresponding DOF in end effector 220 and/or articulated wrist230. In some examples, each of the drive mechanisms 250 may be a cabledisposed inside a hollow sheath or lumen in a Bowden cable likeconfiguration. In some examples, the cable and/or the inside of thelumen may be coated with a low-friction coating such aspolytetrafluoroethylene (PTFE) and/or the like. In some examples, as theproximal end of each of the cables is pulled and/or pushed inside drivesystem 240, such as by wrapping and/or unwrapping the cable about acapstan or shaft, the distal end of the cable moves accordingly andapplies a suitable force and/or torque to adjust one of the DOFs of endeffector 220, articulated wrist 230, and/or surgical instrument 200.

FIG. 3 is a simplified perspective diagram of the distal end of surgicalinstrument 200 according to some embodiments. As shown in FIG. 3 , thedistal end of surgical instrument 200 is depicted so as to showadditional details of end effector 220, articulated wrist 230, and drivemechanisms 250. In more detail, end effector 220 includes opposing jaws310 shown in an open position. Jaws 310 are configured to move betweenopen and closed positions so that end effector 220 may be used during aprocedure to grip and release tissue and/or other structures, such assutures, located at the surgical site. In some examples, jaws 310 may beoperated together as a single unit with both jaws 310 opening and/orclosing at the same time. In some examples, jaws 310 may be openedand/or closed independently so that, for example, one jaw 310 could beheld steady which the other jaw 310 may be opened and/or closed.

FIG. 3 shows that a gripping surface on an inside of each of jaws 310includes a corresponding groove 320, which may act as a guide for acutting blade 330, although the groove 320 may be omitted from one ormore of jaws 310. As cutting blade 330 is extended toward the distal endof end effector 220 and/or retracted toward the proximal end of endeffector 220, each of the grooves 320 may aid in the alignment and/orpositioning of cutting blade 330 during a cutting operation. Extractionand/or retraction of cutting blade 330 is accomplished using a drivecomponent 340 to which cutting blade 330 is attached. In some examples,drive component 340 pushes on cutting blade 330 to extend cutting blade330 and pulls on cutting blade 330 to retract cutting blade 330. Use andpositioning of cutting blade 330 is shown in FIGS. 4A-4C, which aresimplified cut-away diagrams of end effector 220 according to someembodiments. FIG. 4A shows the relationship between cutting blade 330and drive component 340.

End effector 220 further includes a garage feature 350 located at aproximal end of jaws 310. Garage feature 350 includes an opening throughwhich both drive component 340 and cutting blade 330 may pass. Garagefeature 350 is configured to provide a safe storage area for cuttingblade 330 when cutting blade 330 is not in use. Thus, when cutting blade330 is not actively being used as part of a cutting operation, endeffector 220 is configured so that cutting blade 330 may be retractedinto garage feature 350 in a “garaged” or stored position in whichcutting blade 330 is recessed proximally behind jaws 310 as shown inFIG. 4B. Cutting blade 330 may additionally be extended to a position inwhich cutting blade 330 is positioned at or near a distal end of one ofthe grooves 320 as shown in FIG. 4C. In some examples, the positioningof cutting blade 330 as shown in FIG. 4C may correspond to a position ofcutting blade 330 during a cutting operation.

In some examples, end effector 220 and surgical instrument 200 aredesigned so that the default or home position of cutting blade 330 iswithin garage feature 350. This arrangement of garage feature 350 mayprovide several features to end effector 220. In some examples, whencutting blade 330 is retracted into garage feature 350, the sharpcutting edge of cutting blade 330 is effectively sheathed so thatcutting blade 330 is unlikely to accidentally cut tissue during aprocedure and/or medical personnel handling surgical instrument 200and/or end effector 220 before and/or after a procedure. In someexamples, when cutting blade 330 is retracted into garage feature 350,cutting blade 330 may also be protected from damage, such as accidentaldulling, when cutting blade 330 is not actively being used to cut.

Referring back to FIG. 3 , in some embodiments, the gripping surface onthe inside of each of jaws 310 may further include one or more optionalelectrodes 360. In some examples, electrodes 360 may be used to deliverelectrosurgical energy to fuse tissue being held between jaws 310. Insome examples, electrodes 360 may provide an electro-cautery, fusing,and/or sealing feature to end effector 220 so that tissue may be cutand/or fused/sealed using the same surgical tool 200.

In some embodiments, operation of jaws 310, cutting blade 330, and/orthe joints of articulated wrist 230 may be accomplished usingcorresponding ones of the drive mechanisms 250. In some examples, whenjaws 310 are operated independently, a distal end of two of the drivemechanisms 250 (one for each of jaws 310) may be coupled to a respectivejaw 310 so that as the corresponding drive mechanism 250 applies a pulland/or a pushing force (for example, using a cable, lead screw, and/orthe like), the respective jaw 310 may be opened and/or closed. In someexamples, when jaws 310 are operated together, both jaws 310 may becoupled to the distal end of the same drive mechanism 250. In someexamples, drive component 340 may be coupled to a distal end of acorresponding drive mechanism 250 so that forces and/or torques appliedto the corresponding drive mechanism 250 may be transferred to the pushand/or pull motion of drive component 340. In some examples, additionaldrive mechanisms 350 may be used to operate the roll, pitch, and/or yawDOFs in articulated wrist 230.

FIG. 5 is a simplified perspective diagram of a drive unit 500 for adegree of freedom according to some embodiments. According to someembodiments, drive unit 500 may be representative of a portion of thecomponents in drive system 240 of FIG. 2 . As shown in FIG. 5 , driveunit 500 is based on a rotational actuation approach in which a capstan510 is rotated to actuate a DOF. Capstan 510 is coupled to a drive shaft520 which may be the drive shaft of a motor, servo, active actuator,hydraulic actuator, pneumatic actuator, and/or the like (not shown). Astorque is applied to drive shaft 520 and drive shaft 520 and capstan 510are rotated, a cable 530 attached to capstan 510 and/or drive shaft 520may be further wrapped around and/or unwrapped from around capstan 510and/or drive shaft 520. When cable 530 is attached to the proximal endof a corresponding drive mechanism, such as any of drive mechanisms 250,the wrapping and unwrapping of the cable may translate intocorresponding pulling and pushing forces and/or torques that may beapplied to a DOF of an end effector located at the distal end of thedrive mechanism. In some examples, rotation of capstan 510 and driveshaft 520 and the corresponding wrapping and/or unwrapping of cable 530may result in opening and/or closing of gripper jaws such as jaws 310,extending and/or retracting of a cutting blade such as cutting blade330, flexing and/or unflexing of articulated wrist joints, and/or thelike. In some examples, monitoring a rotation angle and/or rotationalvelocity of capstan 510 and/or drive shaft 520 may also provide anindication of a current position and/or velocity of the correspondingDOF coupled to cable 530 through the corresponding drive mechanism.Thus, when drive unit 500 is used in conjunction with the DOFs ofsurgical instrument 200, the rotation angle and/or rotational velocityof capstan 510 and/or drive shaft 520 may provide useful feedback on theangle to which jaws 310 are opened, the position of cutting blade 330,and/or the pitch and/or yaw angle of articulated wrist 230 depending onwhich of the drive mechanisms 250 cable 530 is coupled.

Because it is often desirable for a DOF in an end effector to beconfigured with a default, rest, and/or home position when the DOF isnot being actuated, in some embodiments a drive unit, such as drive unit500 may include some type of resistive and/or restraining mechanism toreturn drive unit 500 to a corresponding home position. In someexamples, use of a home position for a DOF may support configuration ofa surgical instrument, such as surgical instrument 200, where grippingjaws are automatically closed and/or mostly closed, cutting blades areretracted into a garage feature, articulated wrist joints arestraightened, and/or the like. As shown in FIG. 5 , drive unit 500includes a restraining mechanism in the form of a torsion spring 540.Torsion spring 540 is shown attached at one end 550 to capstan 510 andwrapped around capstan 510. As capstan 510 is rotated, a second end 560of torsion spring 540 may freely rotate until it rotates up against astop 570 that may be part of a body of drive unit 500. As capstan 510continues to rotate after the second end 560 of torsion spring 540 isagainst stop 570, torsion spring 540 will begin to provide a restrainingand/or return to home force and/or torque to capstan 510 as dictated bythe amount of rotation of capstan 510 and a spring constant of torsionspring 540. Thus, as greater amounts of rotation are applied to capstan510, torsion spring 540 applies increasing return to home force and/ortorque to capstan 510. It is this return to home force and/or torque oncapstan 510 that may be used, for example, to close the gripping jaws,retract the cutting blade, and/or straighten the articulated wristjoints.

Although FIG. 5 shows the restraining mechanism as a torsion springwrapped around capstan 510, one of ordinary skill would recognize otherpossible restraining mechanisms and/or configurations for therestraining mechanisms to accomplish a similar restraining/return tohome function. In some examples, the body of drive unit 500 may furtherinclude a second stop to provide a return to home force and/or torque tocapstan 510 in an opposite direction to the return to home force and/ortorque resulting from stop 570. In some examples, the second end 560 oftorsion spring 540 may be mounted to the body of drive unit 500 so thatno free movement of torsion spring 540 is permitted before torsionspring 540 begins applying return to home force and/or torque to capstan510 and/or torsion spring 540 applies at least some return to home forceand/or torque to capstan 510 even without rotation of capstan 510.

According to some embodiments, selection of an appropriately sizedrestraining mechanism, such as the spring constant for torsion spring540, for a DOF of an end effector may present several challenges to thedesigner of a surgical instrument. In some situations it may bedesirable to select the size of the restraining mechanism to overcomeany likely and/or reasonable interference with the desired return tohome function of the corresponding drive unit of the DOF. In someexamples, selection of the size of the restraining mechanism to overcomeany likely and/or reasonable interference tends to oversize therestraining mechanism for many of the possible operational scenarios.Additionally, as the size of the restraining mechanism increases, acorresponding greater force or torque has to be applied to the driveunit to overcome the restraining mechanism. In some examples, this mayinclude the use of a larger motor, solenoid, servo, active actuator,hydraulic actuator, pneumatic actuator, and/or the like to overcome therestraining mechanism or result in a smaller operational margin for theDOF that results in less force and/or torque being available to drivethe DOF to perform an operation. For example, less cutting force and/ortorque may be available to apply to a cutting blade to perform a cut. Insome examples, this larger return to home force and/or torque mayincrease the stress and/or strain placed on the drive mechanism that mayresult in increased wear on the drive mechanism, stretching of the drivemechanism, and/or the like. In some examples, the stretching of thedrive mechanism may result in the drive mechanism and the correspondingDOF becoming out of tolerance, thus resulting is a diminished ability tocontrol the DOF as desired. In some examples, this larger return to homeforce and/or torque may increase the likelihood of injury to a patientand/or medical personnel, such as when a return to home gripping forcemay result in damage and/or tearing of tissue still located between thegripping jaws of an end effector.

One possible compromise is to size the restraining mechanism to providesufficient return to home force and/or torque to return the DOF to thehome position when the surgical instrument is not being used (i.e., whenthe surgical instrument is not mounted to a corresponding articulatedarm and/or computer-assisted device) and to use the motor, solenoid,servo, active actuator, hydraulic actuator, pneumatic actuator, and/orthe like coupled to the drive unit to provide additional return to homeforce and/or torque during operational scenarios where additional returnto home force and/or torque is desired. Under this compromise, it isgenerally possible to use smaller motors, solenoids, servos, activeactuators, hydraulic actuators, pneumatic actuators, and/or the likewhile still providing a desired amount of operational margin to supportthe desired operations of the corresponding surgical instrument. In someexamples, the restraining mechanism may be sized to provideapproximately 0 N to 10 N of return to home force and/or a similartorque to the DOF.

FIG. 6 is a simplified diagram of a positional profile 610 and acorresponding torque limit profile 620 for a cutting operation accordingto some embodiments. In some embodiments, positional profile 610 andtorque limit profile 620 may be suitable for application to cuttingblade 330 using drive unit 500. As shown in FIG. 6 , positional profile610 and torque limit profile 620 include a four-phase cutting operationbeginning at a time to. The four phases include an extending phase fromt₀ to t₁, a holding phase from t₁ to t₂, a retracting phase from t₂ tot₃, and a garaging phase from t₃ to t₄. For the purposes of discussingFIG. 6 , the position of the cutting blade will be described relative toan x position of the cutting blade with more positive positions being ina distal direction, however, one of ordinary skill would understand thatthe positions for the cutting blade may be represented using anysuitable positional and/or rotational axis such as a position along anaxis defined by groove 320, a rotational angle of capstan 510, and/orthe like and/or could alternatively be characterized with positivevalues in a more proximal direction.

One of the goals of the extending phase is to rapidly extend the cuttingblade from a retracted position of x_(RET) to an extended position ofx_(EXT). In some examples, x_(RET) may correspond to a garaged and/orhome position of the cutting blade. In some examples, the zero positionfor the cutting blade may correspond to an outer or distal edge of agarage feature, such as garage feature 350, when the articulated wristis in a straight or unflexed position. In some examples, x_(RET) isselected as a sufficiently negative value, such as approximately −3 mm,to account for variability among different drive mechanisms and/or driveunits. In some examples, a negative x_(RET) may also address possibledeviations in the drive mechanism caused by the flexing of thearticulated wrist in the surgical instrument. In some examples, as thearticulated wrist flexes, the drive mechanism may be subject to bendingand/or movement within the hollow shaft (e.g., shaft 210) of thesurgical instrument. As the drive mechanism bends and/or moves aneffective distance, as seen by the drive mechanism, may change betweenthe distal end at the cutting blade and the proximal end at the driveunit. As a result, the amount of retraction to return the cutting bladeto the garage may vary between situations where the articulated wrist isflexed and unflexed. In some examples, x_(EXT) may correspond to a fullyand/or mostly extended position for the cutting blade, such asapproximately +18 mm, so that the cutting blade does not strike the endof a guiding groove, such as one of the grooves 320, and/or to reducethe likelihood of cutting blade exposure where the cutting blade comesout of the guiding grooves and is not able to be retracted back into thegaraged or home position. In some examples, a duration of the extendingphase (i.e., the time between t₀ and t₁) may be rather rapid and mayvary, for example, from 50 ms to 250 ms in length, and preferably 175 msin length.

One of the goals of the holding phase is to continue to command thecutting blade to full extension at x_(EXT) to account for operationalscenarios when it takes longer than the duration of the extending phasefor the cutting blade to transition from x_(RET) to x_(EXT). In someexamples, the holding phase may also reduce the likelihood that thecutting blade will be retracted before it has reached the desiredextension. In some examples, a duration of the holding phase (i.e., thetime between t₁ and t₂) may be similar in magnitude to the duration ofthe extending phase or slightly shorter and may vary, for example, from50 ms to 150 ms in length, and preferably 100 ms in length.

Retraction of the cutting blade may occur using a two-phase operationthat includes the retracting phase and the garaging phase. One of thegoals of the retracting phase is to rapidly retract the cutting blade toa position x_(HLD) that corresponds to retracting the cutting blade to ahold position that is most of the way back to the garaged or homeposition, such as approximately +1 mm. Following the retracting phase,the cutting blade is more completely retracted to the x_(RET) positionduring the garaging phase. In some examples, the use of the two-phaseoperation of retracting followed by garaging may reduce the likelihoodthat the cutting blade may rebound back out the garage during retractionrelative to a single-phase operation directly to x_(RET) and/or reducethe magnitude of loads applied to the cutting blade and drive mechanismduring the garaging phase. In some examples, a duration of theretracting phase (i.e., the time between t₂ and t₃) may vary, forexample, from 50 ms to 175 ms in length, and preferably 120 ms inlength. In some examples, a duration of the garaging phase (i.e., thetime between t₃ and t₄) may vary, for example, from 75 ms to 200 ms inlength, and preferably 150 ms in length.

In some examples, the time periods before to, when the cutting operationbegins, and after t₄, when the cutting operation ends, may correspond toidle phases where the cutting blade is held at the garaged or homeposition of x_(RET) using force and/or torque provided by both therestraining mechanism of the drive unit and the motor, solenoid, servo,active actuator, hydraulic actuator, pneumatic actuator, and/or the likeused to operate the drive unit as is discussed further below.

According to some embodiments, the positional profile 610 of FIG. 6represents a desired position of the cutting blade during a cuttingoperation. In some examples, positional profile 610 may be converted toa time sequence of position commands for the cutting blade and themotor, solenoid, server actuator, hydraulic actuator, pneumaticactuator, and/or the like used to actuate the drive unit for the cuttingblade. In some examples, interpolation and/or curve fitting using, forexample, a cubic spline may be used to determine the time sequence ofposition commands so as to provide a smooth positional profile 610 orposition trajectory for the cutting blade throughout the cuttingoperation. In some examples, the actual position of the cutting bladeand/or the drive unit may be monitored during the cutting operationusing one or more sensors to determine whether the cutting blade and/orthe drive unit are able to follow the positional profile 610. In someexamples, when the cutting blade and/or the drive unit are not able tofollow the positional profile 610 within a predefined tolerance, anaudio, visual, and/or textual alert may be provided to the surgeonand/or other medical personnel to indicate that the cutting operationmay not have been successful. In some examples, the cutting operationmay not be successful when the cutting blade is not able to extend tox_(EXT) and/or becomes exposed and cannot return to x_(RET).

According to some embodiments, even though the cutting blade isgenerally operated using a position control approach as indicated bypositional profile 610, the control unit for the motor, solenoid, servo,active actuator, hydraulic actuator, pneumatic actuator, and/or the likedriving the drive unit for the cutting blade may be subject to upperand/or lower force and/or torque limits. In some examples, the forceand/or torque limits may be determined based on the size of the motor,solenoid, servo, active actuator, hydraulic actuator, pneumaticactuator, and/or the like, to reduce the likelihood of damage and/orexcessive wear to the drive unit, drive mechanism, and/or cutting blade,to reduce power used to actuate the cutting blade, and/or to address thepractical needs of the cutting operation. Torque limit profile 620represents one possible such profile and, although torque limit profile620 is described in terms of torques, other control actuators and/orcontrol systems may alternatively use limits to voltage, current, force,duty cycle, and/or the like as would be understood by one of ordinaryskill in the art.

As shown in FIG. 6 , torque limit profile 620 uses a combination ofthree torque limits depending upon which phase of the cutting operationthe cutting blade is in and/or whether the cutting blade is currentlyidle. And although the torque limits are characterized with a positivetorque limit value corresponding to an extending direction, one ofordinary skill would understand that the sign of the torque limit isarbitrary depending on the configuration of the control actuators and/orthe drive unit for the cutting blade. In torque limit profile 620, atorque limit of TEXT is used during the extending and holding phases ofthe cutting operation. In some examples, TEXT is set at a sufficientlyhigh limit to overcome any restraining mechanism, such as torsion spring540, in the drive unit and to supply suitable actuating force and/ortorque to allow the cutting blade to cut tissue while the cutting bladeis being extended. In some examples, TEXT may be in a range suitable forthe cutting blade to deliver 15 N to 20 N of cutting force duringextension.

A torque limit of T_(RET) is used during the retracting and garagingphases. In some examples, T_(RET) is set at a sufficiently high limit toovercome any tissue and/or other debris from the cutting operation thatmay interfere with the desired retraction and/or garaging of the cuttingblade after cutting has taken place. In some examples, T_(RET) may haveapproximately the same magnitude as TEXT, but with an opposite sign sothat T_(RET) may be in a range suitable for delivering 15 N to 20 N ofretracting force to the cutting blade. In some examples, T_(RET) mayhave a magnitude smaller than that of TEXT to account for the torqueused to overcome the restraining mechanism during extension and toreflect the assistance provided by the restraining mechanism duringretraction.

A torque limit of T_(IDLE) is used when the cutting blade is idle. Insome examples, T_(IDLE) is set to a lower magnitude than T_(RET), butwith a magnitude sufficient to assist the restraining mechanism inkeeping the cutting blade garaged during periods of non-use. In someexamples, the magnitude of TIME may be set to avoid placing excessivestrain on the motor, solenoid, servo, active actuator, hydraulicactuator, pneumatic actuator, drive mechanism, drive, unit, etc. due toattempts to retract the cutting blade beyond any physical limits imposedby the end effector and/or garage feature due to the negative retractionposition of x_(RET). In some examples, T_(IDLE) may be in a rangesuitable for delivering 0 N to 5 N of retracting force to the cuttingblade.

As discussed above and further emphasized here, FIG. 6 is merely anexample which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. According to some embodiments, different positionaland/or torque limit profiles are possible depending upon the desiredoperation of a particular DOF, such as the cutting DOF more directlydiscussed in FIG. 6 . In some examples, different torque limit valuesmay be used in the extending and holding phases and/or in the retractingand garaging phases. In some examples, a more complex torque limitprofile using ramps and/or the like are possible. In some examples, thetorque limit may be variable based on the current position of thecutting blade.

FIG. 7 is a simplified diagram of a method 700 for performing a cuttingoperation according to some embodiments. One or more of the processes710-760 of method 700 may be implemented, at least in part, in the formof executable code stored on non-transient, tangible, machine readablemedia that when run by one or more processors (e.g., the processor 150in control unit 140) may cause the one or more processors to perform oneor more of the processes 710-760. In some embodiments, method 700 may beperformed by an application, such as control application 170. In someembodiments, method 700 may be used to extend and retract a cuttingblade, such as cutting blade 330, of a surgical instrument, such assurgical instrument 200. In some embodiments, the cutting operation ofmethod 700 may be performed according to positional profile 610 and/ortorque limit profile 620. In some embodiments, drive components such asthose described in FIGS. 2, 3, and 4A-4C may be used during theperformance of method 700 to extend, retract, and/or maintain thecutting blade in an idle position.

At a process 710, a cutting blade is maintained in an idle position. Insome examples, the idle position may correspond to a garaged and/or homeposition where the cutting blade is protected from damage and/or thecutting blade is sheathed within a garage feature, such as garagefeature 350, so as to reduce the likelihood of accidentally cuttingtissue and/or medical personnel when active cutting is not taking place.In some examples, the idle position may correspond to a slightlynegative position, such as the position x_(RET) of positional profile610. In some examples, the cutting blade may be held in the idleposition based on force and/or torque applied to the cutting blade by adrive component, a drive mechanism, a drive unit, and/or an actuatorsuch as a motor, solenoid, servo, active actuator, hydraulic actuator,pneumatic actuator, and/or the like. In some examples, the applied forceand/or torque may be applied using a restraining mechanism, such astorsion spring 540, the actuator, and/or both. In some examples, theamount of force and/or torque applied by the actuator may be subject toa limit, such as T_(IDLE) from torque limit profile 620. In someexamples, as long as the cutting blade is not being used for cutting thecutting blade may be maintained in the idle position. In some examples,process 710 may correspond to the periods labeled as idle periods inFIG. 6 .

At a process 720, a cut command is received. In some examples, a surgeonand/or other personnel may request that a cutting operation take place.In some examples, the cutting operation may be requested using one ormore master controls, such as one or more master manipulators, levers,pedals, switches, keys, knobs, triggers, and/or the like located on anoperator console. In some examples, the requested cutting operation maybe received by a control application, such as control application 170,via an interrupt, an input polling operation, an API call, and/or thelike.

At a process 730, the cutting blade is extended. In some examples, afirst phase of the cutting operation may include actuating the cuttingblade to rapidly extend from the idle position of process to 710 to anextended position, such as the position x_(EXT) of positional profile610. In some examples, the actuation of the cutting blade during process730 may include providing a time sequence of position commands to thedrive unit operating the DOF associated with the cutting blade so that asmooth positional profile, such as positional profile 610 during theextending phase, is commanded for the cutting blade. In some examples,the cutting blade may be extended based on force and/or torque appliedto the cutting blade by a drive component, a drive mechanism, a driveunit, and/or an actuator such as a motor, solenoid, servo, activeactuator, hydraulic actuator, pneumatic actuator, and/or the like. Insome examples, the amount of force and/or torque applied to the cuttingblade may be selected so as to overcome any restraining mechanism usedto keep the cutting blade in the idle position as well as to deliversufficient cutting force to cut tissue. In some examples, the amount offorce and/or torque applied may be subject to a limit, such as TEXT fromtorque limit profile 620. In some examples, process 730 may correspondto the period labeled as the extending period in FIG. 6 .

At a process 740, the cutting blade is held in the extended position. Insome examples, a second phase of the cutting operation may includecontinuing to actuate the cutting blade to extend to the extendedposition of process 730. In some examples, this extended position maycorrespond to the position x_(EXT) of positional profile 610. In someexamples, the cutting blade may continue to be extended and/or held atthe extended position based on force and/or torque applied to thecutting blade by a drive component, a drive mechanism, a drive unit,and/or an actuator such as a motor, solenoid, servo, active actuator,hydraulic actuator, pneumatic actuator, and/or the like. In someexamples, the amount of force and/or torque applied to the cutting blademay be selected so as to overcome any restraining mechanism used to keepthe cutting blade in the idle position as well as to deliver sufficientcutting force to cut tissue. In some examples, the amount of forceand/or torque applied may be subject to a limit, such as TEXT fromtorque limit profile 620. In some examples, process 740 may correspondto the period labeled as the hold period in FIG. 6 .

At a process 750, the cutting blade is retracted. In some examples, athird phase of the cutting operation may include actuating the cuttingblade to rapidly retract from the extended position of processes 730and/or 740 to a hold position, such as the position x_(HLD) ofpositional profile 610, located most of the way back toward the idleposition of process 710. In some examples, the actuation of the cuttingblade during process 750 may include providing a time sequence ofposition commands to the drive unit operating the DOF associated withthe cutting blade so that a smooth positional profile, such aspositional profile 610 during the retracting phase, is commanded for thecutting blade. In some examples, the cutting blade may be retractedbased on force and/or torque applied to the cutting blade by a drivecomponent, a drive mechanism, a drive unit, and/or an actuator such as amotor, solenoid, servo, active actuator, hydraulic actuator, pneumaticactuator, and/or the like. In some examples, the amount of force and/ortorque applied to the cutting blade may be selected so as to overcomeany likely tissue, debris, and/or the like that may be interfering withretraction of the cutting blade. In some examples, the retracting mayadditionally be aided by a restraining mechanism used to keep thecutting blade in the idle position. In some examples, the amount offorce and/or torque applied may be subject to a limit, such as T_(RET)from torque limit profile 620. In some examples, process 750 maycorrespond to the period labeled as the retracting period in FIG. 6 .

At a process 760, the cutting blade is garaged. In some examples, afourth phase of the cutting operation may include actuating the cuttingblade to retract from the hold position of process 750 to the idleposition of process 710. In some examples, the actuation of the cuttingblade during process 760 may include providing a time sequence ofposition commands to the drive unit operating the DOF associated withthe cutting blade so that a smooth positional profile, such aspositional profile 610 during the garaging phase, is commanded for thecutting blade. In some examples, the cutting blade may be retractedbased on force and/or torque applied to the cutting blade by a drivecomponent, a drive mechanism, a drive unit, and/or an actuator such as amotor, solenoid, servo, active actuator, hydraulic actuator, pneumaticactuator, and/or the like. In some examples, the amount of force and/ortorque applied to the cutting blade may be selected so as to overcomeany likely tissue, debris, and/or the like that may be interfering withgaraging of the cutting blade. In some examples, the garaging mayadditionally be aided by a restraining mechanism used to keep thecutting blade in the idle position. In some examples, the amount offorce and/or torque applied may be subject to a limit, such as T_(RET)from torque limit profile 620. In some examples, process 760 maycorrespond to the period labeled as the garaging period in FIG. 6 .

After the cutting blade is garaged during process 760, the cuttingoperation is complete and the cutting blade is maintained in the idleposition using process 710 until another cutting command is received.

Although not shown in FIG. 7 , one of ordinary skill would understandthat method 700 may be performed in cooperation with one or moremonitoring and/or reporting processes. In some examples, the actualposition of the cutting blade and/or the drive unit for the cuttingblade may be monitored using one or more sensors during method 700 todetermine whether the cutting blade and/or the drive unit are able tofollow the positional profile for the cutting blade, such as thepositional profile 610. In some examples, when the cutting blade and/orthe drive unit are not able to follow the positional profile within apredefined tolerance, an audio, visual, and/or textual alert may beprovided to the surgeon and/or other medical personnel to indicate thatthe cutting operation may not have been successful. In some examples,the cutting operation may not be successful when the cutting blade isnot able to extend as commanded during processes 730 and/or 740. In someexamples, the cutting operation may not be successful when the cuttingblade becomes exposed and cannot return to the garage. In some examples,a warning and/or an alert using one or more audio, visual, and/ortextual alerts may be issued when any of the extracting, holding,retracting, and/or garaging operations reach one of the force and/ortorque limits corresponding to the respective cutting operation phase.

Some examples of control units, such as control unit 140 may includenon-transient, tangible, machine readable media that include executablecode that when run by one or more processors (e.g., processor 150) maycause the one or more processors to perform the processes of method 700.Some common forms of machine readable media that may include theprocesses of method 700 are, for example, floppy disk, flexible disk,hard disk, magnetic tape, any other magnetic medium, CD-ROM, any otheroptical medium, punch cards, paper tape, any other physical medium withpatterns of holes, RAM, PROM, EPROM, FLASH-EPROM, any other memory chipor cartridge, and/or any other medium from which a processor or computeris adapted to read.

Although illustrative embodiments have been shown and described, a widerange of modification, change and substitution is contemplated in theforegoing disclosure and in some instances, some features of theembodiments may be employed without a corresponding use of otherfeatures. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. Thus, the scope of theinvention should be limited only by the following claims, and it isappropriate that the claims be construed broadly and in a mannerconsistent with the scope of the embodiments disclosed herein.

What is claimed is:
 1. A computer-assisted device comprising: one ormore processors; a motor or other active actuator; and an articulatedarm configured to support an instrument having a cutting blade; whereinthe one or more processors are configured to control, using the motor orother active actuator, the instrument according to a force or torquelimit profile; wherein the force or torque limit profile comprises: afirst force or torque limit used when extending the cutting blade from afirst position to a second position; a second force or torque limit usedwhen retracting the cutting blade from the second position to a thirdposition between the first position and the second position and furtherretracting the cutting blade to the first position; and a third force ortorque limit used while the cutting blade is in the first position. 2.The computer-assisted device of claim 1, wherein one or more of grippingjaws of the instrument include a groove to assist in guiding the cuttingblade during the extending and retracting.
 3. The computer-assisteddevice of claim 1, wherein the first position is within a garage of theinstrument.
 4. The computer-assisted device of claim 1, wherein thethird position corresponds to a position where the cutting blade isretracted to just outside a garage of the instrument.
 5. Thecomputer-assisted device of claim 1, wherein the one or more processorsare further configured to control, using the motor or other activeactuator, the cutting blade to follow a positional profile subject tothe first, second, and third force or torque limits, the positionalprofile comprising a time sequence of desired positions describing asmooth trajectory for the cutting blade between the first, second, andthird positions.
 6. The computer-assisted device of claim 5, wherein thepositional profile comprises a holding phase for holding the cuttingblade in the second position before retracting the cutting blade to thethird position.
 7. The computer-assisted device of claim 5, wherein thepositional profile comprises a phase for holding the cutting blade inthe third position before further retracting the cutting blade to thefirst position.
 8. The computer-assisted device of claim 1, wherein amagnitude of the first force or torque limit and a magnitude of thesecond force or torque limit is a same force or torque limit magnitude.9. The computer-assisted device of claim 1, wherein a magnitude of thefirst force or torque limit is greater than a magnitude of the secondforce or torque limit.
 10. The computer-assisted device of claim 1,wherein a magnitude of the third force or torque limit is lower than amagnitude of the second force or torque limit.
 11. The computer-assisteddevice of claim 1, wherein a difference between a magnitude of the firstforce or torque limit and a magnitude of the second force or torquelimit is based on a force or torque applied by a restraining mechanismused to help maintain the cutting blade in the first position.
 12. Amethod of operating a cutting instrument, the method comprising:controlling, by a control unit using a motor or other active actuator, adrive unit of an instrument according to a force or torque limitprofile, wherein the force or torque limit profile comprises: a firstforce or torque limit used when extending a cutting blade of theinstrument from a first position to a second position; a second force ortorque limit used when retracting the cutting blade from the secondposition to a third position between the first position and the secondposition and further retracting the cutting blade to the first position;and a third force or torque limit used while the cutting blade is in thefirst position.
 13. The method of claim 12, wherein the first positionis within a garage.
 14. The method of claim 12, wherein the thirdposition corresponds to a position where the cutting blade is retractedto just outside a garage.
 15. The method of claim 12, further comprisingcontrolling, by the control unit using the motor or other activeactuator, the cutting blade to follow a positional profile subject tothe first, second, and third force or torque limits, the positionalprofile comprising a time sequence of desired positions describing asmooth trajectory for the cutting blade between the first, second, andthird positions.
 16. The method of claim 12, wherein a differencebetween a magnitude of the first force or torque limit and a magnitudeof the second force or torque limit is based on a force or torqueapplied by a restraining mechanism used to help maintain the cuttingblade in the first position.
 17. A non-transitory machine-readablemedium comprising a plurality of machine-readable instructions whichwhen executed by one or more processors associated with acomputer-assisted device are adapted to cause the one or more processorsto perform a method comprising: controlling, using a motor or otheractive actuator, a drive unit of an instrument according to a force ortorque limit profile, wherein the force or torque limit profilecomprises: a first force or torque limit used when extending a cuttingblade of the instrument from a first position to a second position; asecond force or torque limit used when retracting the cutting blade fromthe second position to a third position between the first position andthe second position and further retracting the cutting blade to thefirst position; and a third force or torque limit used while the cuttingblade is in the first position.
 18. The non-transitory machine-readablemedium of claim 17, wherein: the first position is within a garage; andthe third position corresponds to a position where the cutting blade isretracted to just outside the garage.
 19. The non-transitorymachine-readable medium of claim 17, wherein the method furthercomprises controlling, using the motor or other active actuator, thecutting blade to follow a positional profile subject to the first,second, and third force or torque limits, the positional profilecomprising a time sequence of desired positions describing a smoothtrajectory for the cutting blade between the first, second, and thirdpositions.
 20. The non-transitory machine-readable medium of claim 17,wherein a difference between a magnitude of the first force or torquelimit and a magnitude of the second force or torque limit is based on aforce or torque applied by a restraining mechanism used to help maintainthe cutting blade in the first position.